This invention relates to the cooling means of an electric machine, and more particularly to an electric motor having its housing and armature shaft provided with circulating passageways for cooling oil in order to prevent overheating during operation.
One of the most common and important problems in the application of machines is the temperature rise resulting from various losses, such as copper losses, brush-contact loss, core loss, mechanical loss, stray load loss, etc. And, as well known in the art, the operating temperature of a machine is closely associated with its life expectancy, because deterioration of the insulation is a function of both time and temperature. Such deterioration is a chemical phenomenon involving slow oxidation and brittle hardening and leading to loss of mechanical durability and dielectric strength. Therefore, various cooling means or ventilating systems are proposed for such machines to remove the heat arising from the inevitable losses, and thus to prevent overheating of the machines.
Of the many types of cooling means available, the most common are cooling fans. However, the cooling problem in electric machines in general increases in difficulty with increasing size. This problem is a particularly serious one in large machines, where economy, mechanical requirements, shipping, and erection all demand compactness. Therefore, the conventional type of cooling fan can not ensure that the cooling air will effectively remove the heat arising from the losses; and in a machine of this type, deterioration of the insulation and burning of brush or coil windings still frequently occur thereby reducing its life.